function rule_applicable(word, pos, consumed, rule) {
    for(let i=0; i<rule.length; i++) {
        if((word[pos+i] != rule[i]) | (consumed[pos+i] == true)) {
            return false;
        }
    }
    return true;
}


function generate(start, rules, iterations) {
    if(iterations == 0) {
        return start;
    }

    var word = start;
    var consumed = new Array(word.length);
    for(let rule of rules) {
        let pos = 0;
        var newword = [];
        var newconsumed = [];
        while(pos < word.length) {
            if(rule_applicable(word, pos, consumed, rule[0])) {
                var ruleres;
                if(typeof rule[1] == 'function') {
                    ruleres = rule[1]();
                } else if(typeof rule[1] == 'object') {
                    var r = Math.floor(Math.random() * rule[1].length);
                    ruleres = rule[1][r];
                }else {
                    ruleres = rule[1];
                }
                newword += ruleres;
                for(let i=0; i<ruleres.length; i++) {
                    newconsumed.push(true);
                }
                pos += rule[0].length;
            } else {
                newword += word[pos];
                newconsumed.push(false);
                pos += 1;
            }
        }
        word = newword;
        consumed = newconsumed;
    }

    return generate(newword, rules, iterations - 1);
}


function draw_initstate(grp, state) {
    if(!('dir' in state)) {
        state.dir = 0;
        state.turnnoise = 0;
        state.lennoise = 0;
        state.pos = new paper.Point(0, 0);
        state.pathstack = [];
        state.stepsize = 1;
        state.stack = [];
        state.curpath = null;
    }

    /*
      for(let i=0; i<10; i++) {
      var color = new paper.Color(255,255,255);
      color.saturation = 1;
      color.brightness = 1;
      color.hue = 36 * (10-i); // TODO remove constant
      state.palette.push(color);
      }
    */
    state.palette = [
        new paper.Color('#ff0000'),
        new paper.Color('#ff0000'),
        new paper.Color('#ff00ff'),
        new paper.Color('#ff00ff'),
        new paper.Color('#0000ff'),
        new paper.Color('#0000ff'),
        new paper.Color('#00ff00'),
        new paper.Color('#00ff00'),
    ];
}


function draw_set_dir(dir) {
    return function(p, state) {
        state.dir = dir;
    };
}


function draw_set_turn_noise(level) {
    return function(p, state) {
        state.turnnoise = level;
    };
}


function draw_set_length_noise(level) {
    return function(p, state) {
        state.lennoise = level;
    };
}


function draw_forward(factor=1) {
    return function(grp, state) {
        if(state.curpath == null) {
            var p = new paper.Path();
            p.add(state.pos);
            state.curpath = p;
            // index 0 corresponds to empty state.stack
            if(state.pathstack[state.stack.length] == null) {
                var cp = new paper.CompoundPath();
                cp.addChild(p);
                cp.strokeColor = state.palette[state.stack.length];
                state.pathstack[state.stack.length] = cp;
                grp.addChild(cp);
            }
            state.pathstack[state.stack.length].addChild(p);
        }

        var lastp = state.curpath.segments[state.curpath.segments.length - 1].point;
        var noise = 1 + (Math.random() - 0.5) * state.lennoise;
        state.curpath.add(lastp.add(new paper.Point(
              Math.sin(state.dir) * state.stepsize * factor * noise,
              Math.cos(state.dir) * state.stepsize * factor * noise
        )));
        var lastseg = state.curpath.segments[state.curpath.segments.length - 1];
        state.pos = lastseg.point;
    };
}


function draw_stepsize_mul(factor) {
    return function(p, state) {
        if(typeof factor == 'function') {
            var f = factor();
        } else {
            var f = factor;
        }
        state.stepsize *= f;
    };
}


function draw_turn(angle) {
    return function(p, state) {
        state.dir += angle;
    };
}


function draw_angle_turn(fac) {
    return function(p, state) {
        var a = state.angle * (1 + (Math.random() - 0.5) * state.turnnoise);
        state.dir += a * fac;
    };
}


function draw_angle_init(angle) {
    return function(p, state) {
        state.angle = angle;
    };
}


function draw_angle_add(delta) {
    return function(p, state) {
        state.angle += delta;
    };
}


function draw_state_push() {
    return function(grp, state) {
        state.stack.push({
            pos: state.pos,
            dir: state.dir,
            stepsize: state.stepsize,
        });
        state.curpath = null;
        /*
        if(state.palette[state.stack.length] !=
           state.palette[state.stack.length - 1]) {
            p.addChild(new paper.Path());
            state.curpath = p.lastChild;
            state.curpath.add(pos);
            state.curpath.strokeColor = state.palette[state.stack.length];
        }
        */
    };
}


function draw_state_pop() {
    return function(grp, state) {
        var s = state.stack.pop();
        state.dir = s.dir;
        state.stepsize = s.stepsize;
        state.pos = s.pos;
        state.curpath = null;
    };
}


function draw(word, actions) {
    var grp = new paper.Group();
    var state = {};
    draw_initstate(grp, state);
    for(let w of word) {
        if(w in actions) {
            actions[w](grp, state);
        }
    }
    return grp;
}